The goal of this project is to investigate genetic mechanisms involved in neuronal plasticity. Specifically, I propose to examine, at the molecular level, mechanisms involved in regulating neurotransmitter genes in dissociated sympathetic ganglion cultures. A cloned probe for tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, will be used to study the regulation and expression of its gene in vitro. Tyrosine hydroxylase mRNA levels and rate of transcription will be determined under various conditions known to influence the enzyme levels. In particular, I will determine the effects of nerve growth factor, glucocorticoids, elevanted K+ and various other factors on synthesis rates and mRNA levels for this enzyme. This data will be correlated with tyrosine hydroxylase enzyme levels determined in matched cultures. These studies will be extended to investigate the regulation of tyrosine hydroxylase under conditions inducing a cholinergic phenotype. Experiments will focus on what role conditioned medium, glucocorticoids and epidermal growth factor play in eliciting this phenotypic switch. Also, I will examine whether these are post-transcriptional or post-translational effects using the TH cloned probe and enzyme number determinations. Results from these studies will further our knowledge of how cells become committed to differentiation and what are some of the factors involved.